Variety of expiratory resistance between different CPAP devices for preterm infants
Introduction: Several CPAP systems for preterm infants are currently in use. Some work with conventional ventilators, others use a jet ventilation system. It is assumed that the most important advantage of jet-CPAP systems is a lower expiratory resistance. In this study we investigated the expiratory resistance of seven different CPAP systems. Methods: We studied two primary-care CPAP systems, 3 jet-CPAP generators and 2 conventional CPAP devices. All devices were adjusted at 6mbar and connected with a test lung simulating a standardized expiration volume of 6ml within 0.8sec. The expiratory resistance was defined as the maximum pressure increase during the expiration period measured upstream of the CPAP generator. Results: In primary-care CPAP devices the pressure during the expiration period increased by 0.18mbar (SD 0.02) against the Benveniste valve and by 0.61mbar (SD 0.02) against the Neopuff. In jet-CPAP devices the pressure increased by 0.10mbar (SD 0.02) against the Infant Flow, by 0.63mbar (SD 0.02) against the Medijet REF 1000 and by 0.21mbar (SD 0.05) against the Medijet REF 1010. In conventional CPAP systems the pressure increased by 0.43mbar (SD 0.02) against the Baby-Flow and by 0.46mbar (SD 0.06) against the Bubble-CPAP. Conclusion: All CPAP devices showed a pressure increase during the expiration period, which shows that they all created an expiratory resistance. Jet-CPAP devices did not produce lower expiratory resistance than conventional CPAP devices. However, as the main purpose of CPAP systems is to create pressure, the clinical relevance of a small pressure increase during the expiration period must be discussed critically.